An essential nutrient for the body, vitamin E is made up of four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta), with the difference between tocotrienols and tocopherols lying in the unsaturated side chain having three double bonds in its farnesyl isoprenoid tail for tocotrienols whereas these double bonds are single bonds in the tocopherols (FIG. 1).
Tocotrienols occur in selected vegetable oils such as palm and rice bran, certain types of fruits such as annatto and saw palmetto, nuts such as macadamia and plant products such as rubber tree latex. The tocotrienol component of the total Vitamin E is generally lower than the tocopherol component.
Chemically, each of the tocotrienol and tocopherol isomers have an antioxidant activity due to their ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring to a free radical in the body. This process inactivates (“quenches”) the free radical by effectively donating a single unpaired electron (which comes with the hydrogen atom) to the radical.
Vitamin E has long been known for its antioxidative properties against lipid peroxidation in biological membranes and alpha-tocopherol has previously been Considered to be the most active form. However, in vivo, tocotrienols are more powerful antioxidants, and lipid oxygen radical absorbance capacity (ORAC) values are highest for delta-tocotrienol. Recent data would suggest that tocotrienols are better antioxidants than tocopherols at preventing cardiovascular diseases and cancer, and in the treatment of diabetes. Current formulations of vitamin E supplements are composed mainly of alpha-tocopherol.
Tocotrienols have many uses beyond their lipid-soluble antioxidant property. They specifically inhibit biosynthesis of cholesterol by the liver through enhanced degradation of the enzyme HMG-CoA reductase (Song et al “Insig dependent ubiquitination and degradation of 3-hydroxy-3-methylglutaryl coenzyme a reductase by delta- and gamma-tocotrienols” The Journal of Biological Chemistry 281 (35):25054-61). Tocotrienols have been shown to inhibit inflammatory pathways mediated by NF-κB (Nesaretnam et al “Tocotrienols: inflammation and cancer” Ann NY Acad Sci. 2011 July; 1229:18-22). They have also been identified as agonists to peroxisome proliferator-activated receptor (PPAR), in particular PPAR-gamma, which is an insulin-sensitiser in addition to increasing adipogenesis (Fang et al “Vitamin E tocotrienols improve insulin sensitivity through activating peroxisome proliferator-activated receptors” Mol Nutr Food Res 2010 March; 54(3):345-52). Indeed, tocotrienols influence many more biochemical pathways than tocopherols, and are being developed as treatments for inflammation, ischaemia-associated diseases such as stroke and myocardial infarct, dyslipidaemia and even cancer (Khosla et at “Postprandial levels of the natural vitamin E tocotrienol in human circulation” Antioxidants & Redox Signalling 8(5-6): 1059-68).
Tocotrienols have been shown to or have the potential to:                have strong anti-oxidant properties (Serbinova et al “Free radical recycling and intramembrane mobility in the antioxidant properties of alpha-tocopherol and aplpha-tocotrienol” Free Radical Biology & Medicine 10(5):263-75).        reverse hypertension and cardiac fibrosis (Black et at “Palm tocotrienols protect ApoE +/− mice from diet induced atheroma formation” J Nutrition 2000; 130(10):2420-6).        improve control of blood glucose and insulin response (Kuhad et at (2009) “Suppression of NF-κβ signalling pathway by tocotrienol can prevent diabetes associated cognitive defects” Pharmacology Biochemistry, and Behaviour 92(2):251-9)        specifically inhibit biosynthesis of cholesterol by the liver, i.e., they can lower cholesterol levels and ameliorate dyslipidaemia (Song et al “Insig dependent ubiquitination and degradation of 3-hydroxy-3-methylglutaryl coenzyme a reductase by delta- and gamma-tocotrienols” The Journal of Biological Chemistry 281 (35):25054-61)        inhibit inflammatory pathways mediated by cyclooxygenase-2 and 12-lipoxygenase, i.e., they can be used as treatments for inflammation (Khanna et at “Molecular basis of vitamin E action: tocotrienol modulates 12-lipoxygenase, a key mediator of glutamate induced neurodegeneration” J Biol Chem 2003; 278:43508-43515)        potentially be useful as treatments for stroke, myocardial infarct, and even cancer (Hussein et al “d-Delta-tocotrienol-mediated suppression of the proliferation of human PANC-1, MIA PaCa-2, and BxPC-3 pancreatic carcinoma cells” Pancreas 38(4):e124-36)        improve exercise endurance and improve muscle glycogen levels (Lee et at “Effects of tocotrienol-rich fraction on exercise endurance capacity and oxidative stress in forced swimming rats” Eur J Appl Physiol 2009; 107(5):587-95)        act as radioactive countermeasures for persons exposed to radiation (Ghosh et at “Gamma-tocotrienol, a tocol antioxidant as a potent radioprotector” Int J Radiat Biol 85(7): 598-606)        
Dietary lipids and fat-soluble vitamins must first be emulsified by bile and packaged into micelles for transport into the circulation to be absorbed from the gastrointestinal tract. Bile excretion is dependent on the level and type of dietary fat consumed, and studies have shown that tocotrienol absorption is reduced in fasted versus full-fed individuals (Yap et at “Pharmacokinetics and biovailability of alpha-, gamma- and delta-tocotrienols under different food status” J Pharm Pharmacol 2001 January; 53(1):67-71). Oral administration of isolated tocotrienols by gavage or gel capsules may therefore lack sufficient fat content to stimulate enough bile excretion into the small intestine that would be necessary to promote tocotrienol absorption.
Following oral administration, tocotrienols are absorbed from the intestine and transported to the systemic circulation through the lymphatic pathway. Studies in humans have shown that gamma-tocotrienol relative bioavailability increased when administered with food and that in the fasted human, plasma tocotrienol concentration do not significantly increase following tocotrienol ingestion (Yap et al “Pharmacokinetics and biovailability of alpha-, gamma- and delta-tocotrienols under different food status” J Pharm Pharmacol 2001 January; 53(1):67-71). Although food enhances gamma-tocotrienol absorption by stimulating excretion of bile and pancreatic enzymes that enhance the formation of mixed micelles, gamma-tocotrienol absorption remains limited and far from complete.
It would appear that it is very difficult to obtain and/or sustain therapeutic levels of gamma-tocotrienol in the blood and target tissues by simple oral administration because absorption and transport mechanisms within the body are extremely limiting and display significant preference for alpha-tocopherol. Although various tocotrienol-containing products are already commercially available, these products are simply capsules filled with a blend of various tocopherols and tocotrienol oils and sold as nutritional supplements for oral consumption. This type of formulation or delivery system displays poor solubility in the fluids of the intestine and high oral doses of tocotrienols inhibit its own absorption from the gut. Consequently, only relatively low levels of tocotrienol will reach the blood when simply formulated as an oil-filled capsule delivery system and hence one strategy that is in current use is to use an emulsifying agent to enhance absorption from the gastrointestinal tract.
Tocotrienols can be associated with the lipoprotein particles termed chylomicrons and taken up via the gut lacteal system where they are transported via the lymphatic system to the circulation. From here, the degree of uptake by tissues varies. Some reports say that the majority ends up in skin and adipose tissue, with lower uptake into other tissues (Gee, P. T., “Unleashing the untold and misunderstood observations on vitamin E” Genes & Nutrition February 2011, Vol 6, Issue 1, p 5-16). They can be incorporated into very low density lipoproteins at least in part mediated by binding to alpha-tocopherol transport protein to be taken up into the liver and repackaged into lipoproteins for export to other tissues via the circulation. For example, gamma-tocotrienol and delta-tocotrienol seem to have very low levels of uptake by key metabolic tissues such as skeletal muscle and liver.
Tocotrienol supplementation did not appear to confer a therapeutic effect in moderate-sized clinical trials in patients with dyslipidaemia, despite the fact that plasma tocotrienols were elevated by the oral supplementation. This may have been due to inadequate dosage, the competitive effects of the alpha-tocopherol that were co-supplemented, or insufficient levels of tocotrienols being present in the liver so as to inhibit biosynthesis of cholesterol). This meant that reports of positive effects were restricted to rodent studies and some small human trials. It has therefore been doubted as to whether the beneficial effects found in animal studies could be translated to humans, and whether absorbtion/storage of tocotrienols was deficient. It is also clear that alpha-tocopherol has the highest affinity for the transport protein (named alpha-tocopherol transport protein-alpha-TTP) and that tocotrienols appear to be more rapidly metabolised than alpha tocopherol, perhaps due to their unsaturated isoprenoid tail and reduced stabilization by alpha-TTP due to competition from alpha-tocopherol. It was thought that the lack of any beneficial effect being observed in these studies was either due to the poor bioavailability of orally delivered tocotrienols, or the competitive effects of alpha-tocopherol present in the compositions or a combination of both of these factors.
Given the potential clinical benefits of tocotrienols, and their low toxicity (Nakamura et al, “Oral Toxicity of a tocotrienol preparation in rats” Food Chem Toxicol 2001 August; 39(8): 799-805), it would be useful to provide formulations of tocotrienols with higher bioavailablity than has been possible to date. Attempts have been made to improve the bioavailability of tocotrieniols by incorporating them into lipid nanoparticles or transferrin-bearing multilamellar vesicles, which appears to enhance the antitumour effect of tocotrienols by up to 70-fold (Fu et al, “Novel tocotrienol-entrapping vesicles can eradicate solid tumours after intravenous administration” J Control Release 2011 Aug. 25; 154(1):20-6). However, such formulations are limited in that they must be introduced intravenously (which is not practical or suitable for non-clinical applications and have limited market acceptance for all but the most serious and life-threatening therapeutic indications) and are dependent upon the use of tocophetyl based multilamellar vesicles which may themselves interfere with the activity of the tocotrienols present.
There is a relatively low availability and uptake of tocotrienols into key metabolic tissues such as muscle and liver via oral administration. In a recent paper, supplementation of 400 mg tocotrienols per day for 12 weeks only achieved low or sub-nanomolar/g levels in tissues, and the blood level remained below 2 umol/L in all males. (Patel et al, “Oral tocotrienols are transported to human tissues and delay the progression of a model of end-stage liver disease”, Journal of Nutrition 2012, 142 (3): 512-519). Therefore the need exists for a method of delivering higher levels of tocotrienols into these tissues while minimising metabolic degradation by the liver.